1. Field of the Invention
The invention relates to a method for signalling an energizing coil of a solenoid-operated reciprocating plunger pump as set forth in the preamble of claim 1.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
One such method of signalling an energizing coil of a solenoid-operated reciprocating plunger pump is known from PCT/EP 93/00494. In this method a current control circuit is employed which controls the energizing current flowing through the energizing coil 600 (FIG. 1) as a function of the current setpoint in the form of a current or voltage setting. The energizing coil 600 is connected to a power transistor 601 which is connected to ground via a precision resistor 602, a comparator 602 being connected by its output to the control input of the transistor 601, for example, to the base of the transistor. The non-inverting input of the comparator 603 receives the current setpoint, obtained for example by means of a microcomputer. The inverting input of the comparator 603 is connected to one side of a resistor which is connected to the transistor 601. This circuit is a bang-bang control system which limits the current flowing through the energizing coil as a maximim, depending on the applied current setpoint, ON/OFF action of the power transistor 601 chopping roughly delta-shaped the current flow through the energizing coil in the control range.
In this application of the method the current setpoint is applied in the form of square wave pulses to the comparator 603, the length of the pulses dictating the duration of the corresponding energizing pulse and the amplitude of the pulse dictating the maximum current flowing through the energizing coil.
By this method different amounts of fuel can be metered by the reciprocating plunger pump operating more or less independently of coil heating and fluctuations in the supply voltage.
From DE 28 41 781 C2 a means for operating electromagnetic devices in internal combustion engines, more particularly solenoid valves in fuel supply systems, is known. This means controls the current profile of an injection signal at the start of the injection pulse to an excessively high value ensuring that the solenoid valve is opened and holds the current constant at a value slightly below the peak value attained at the start.
In DE 37 22 527 A1 a method of signalling an injector for an internal combustion engine is described in which the energizing coil of the injector is signalled in a way similar to the method as described in DE 28 41 781 C2, whereby, however, at the end of the injection pulse a transition is made from a chopped current regulation, during which the current value oscillates between two threshold values, to a current regulation having a constant current value so that the injector is closed at a precisely predetermined point in time in OFF action, i.e. at the end of the current pulse.